In recent years, there is proposed an electric power steering device of an electromechanical integrated structure in which motor windings of total three or more phases are provided in one motor housing, total two power conversion units are provided in a housing of a power conversion device, and these housing are connected to each other. An example of a system of the electromechanical integrated structure is disclosed in PTL 1. In addition, a PWM control is well known as a scheme of controlling the three-phase motor using a DC power source and the power conversion unit. In the PWM control, a current value flowing the motor and a motor rotation speed are detected, and a voltage command value to the power conversion unit is calculated on the basis of a command value given from a host and the detection result, so that torque of the motor and the motor rotation speed can be controlled to a desired value.
Herein, a detection method in which the power conversion unit and a wiring unit electrically connected to the motor are used to detect will be exemplified as a method of detecting the current flowing to each phase of the motor. However, in such a method, there should include three current detectors and detection wirings in each of two power conversion units, and further include operational amplifiers in a control unit to amplify the values obtained from detectors. Therefore, the power conversion device is increased in size, and a connecting process becomes burden.
Another method of detecting the current flowing to each phase of the motor is disclosed in PTL 2 for example. The technique disclosed in PTL 2 is a scheme of obtaining the current value flowing to each phase of the motor using only one current detector by synchronizing the PWM switching period of each phase with a current detection timing of the current detector. In addition, the technique is a scheme in which a correction control is performed to make an average value of voltage vectors Vs′ and Vs″ to be equalized with a voltage vector Vs so as to secure time for detecting the current and to obtain the current value flowing to the respective phases of the motor when the switching timings of the respective phases of the power conversion units approach each other, and there is secured no sufficient time for the current detector to detect the current. A control technique for realizing the detection by equalizing the average value of the voltage vectors Vs′ and Vs″ with the voltage vector Vs will be referred to as “harmonic wave superposition system”.